Our overall aim is to apply solid state NMR to oriented collagen fibrils, nature~s most abundant protein and to develop this technique for studying fibrous proteins and other macromolecular structures not amenable to x-ray diffraction or solution NMR methods. We propose to use solid state 2H, 13C and 15N NMR spectroscopy of collagen fibrils to directly determine essential elements of this important protein~s secondary structure. These studies make use of oriented fiber and magic angle spinning (MAS) methods. Structural features to be determined are the average orientation of individual peptide planes of the collagen tripeptide repeat relative to e fiber axis and the location of structural waters. The measurement and interpretation of 13C, 17O and 15N chemical shift parameters will be further developed with regard to a general method for determining secondary structure in solid proteins. Collagen provides the proteinaceous matrix for bone, it is the dominant material in and responsible for the tensile strength of tendons and it maintains the structural integrity of veins and arteries. In more than 90% of the cases of children with the heritable disorder of osteogenesis imperfecta, there is a mutation in the genes for type I procollagen. Clini l symptoms include extreme bone fragility, hypermobility and congenital dislocation of joints, osteoarthritis, osteoporosis and skin abnormalities. The architecture of the supramolecular collagen assembly is particularly sensitive to mutations which disrupt the structure of the collagen molecule anywhere along its 3000 A length, thus the collagen molecular structure is fundamental. We anticipate that these experiments will define the range of conformations that are allowed in the collagen triple helical motif.